Recent studies have suggested that an oral dose of acetylcysteine could play a prophylactic role in the prevention of nephrotoxicity from iodine contrast media in patients affected by chronic renal failure. Between June 2001 and September 2002 we selected 120 patients with a basal plasma creatinine level greater than 1.36 mg/dl investigated by coronary angiography. The treatment group included 60 patients who received 600 mg of acetylcysteine in the morning and evening before the day of the examination together with intravenous saline hydration. The control group patients received hydration alone. The clinical characteristics of the groups were comparable as well as the basal plasma creatinine level: 2.01+/-1.1 mg/dl in the acetylcysteine group and 1.81+/-0.69 in the control group. The plasma creatinine level was measured 24 and 48 hours after coronary angiography. The respective changes in plasma creatinine level at 24 and 48 hours were 0.12+/-0.29 and 0.02+/-0.29 mg/dl in the acetylcysteine group and 0.06+/-0.29 and 0.07+/-0.43 mg/dl in the control group (NS). Acute renal failure caused by the contrast medium, defined by an increase of 25% in the plasma creatinine level compared to the basal value, occurred in 3 patients from the acetylcysteine group and 2 patients from the control group. The only predictive factor for acute renal failure was the quantity of contrast medium (316+/-141 vs 173+/-115 ml, p<0.05). In conclusion, acute renal failure caused by contrast medium is rare in sufficiently hydrated patients with moderate chronic renal failure when a low dose of contrast medium is used. Our study does not confirm a prophylactic effect of acetylcysteine in the prevention of nephrotoxicity from contrast media following coronary angiography in patients with moderate chronic renal failure.